US9708725B2 - Method for maintenance of used permanent cathode plates - Google Patents

Method for maintenance of used permanent cathode plates Download PDF

Info

Publication number
US9708725B2
US9708725B2 US15/104,312 US201415104312A US9708725B2 US 9708725 B2 US9708725 B2 US 9708725B2 US 201415104312 A US201415104312 A US 201415104312A US 9708725 B2 US9708725 B2 US 9708725B2
Authority
US
United States
Prior art keywords
grain boundaries
cathode plate
plate
grinding
regenerating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
US15/104,312
Other versions
US20160312376A1 (en
Inventor
Mari Lindgren
Henri K. Virtanen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Metso Finland Oy
Original Assignee
Outotec Finland Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Outotec Finland Oy filed Critical Outotec Finland Oy
Assigned to OUTOTEC (FINLAND) OY reassignment OUTOTEC (FINLAND) OY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: LINDGREN, MARI, VIRTANEN, HENRI K.
Publication of US20160312376A1 publication Critical patent/US20160312376A1/en
Application granted granted Critical
Publication of US9708725B2 publication Critical patent/US9708725B2/en
Assigned to Metso Outotec Finland Oy reassignment Metso Outotec Finland Oy CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: METSO MINERALS OY
Assigned to METSO MINERALS OY reassignment METSO MINERALS OY MERGER (SEE DOCUMENT FOR DETAILS). Assignors: OUTOTEC (FINLAND) OY
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C25F3/06—Etching of iron or steel
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/02—Electrodes; Connections thereof
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/06—Operating or servicing

Definitions

  • the present invention relates to a method for maintenance of used permanent cathode plates.
  • electrolytic refining When the intention is to manufacture pure metal such as copper, hydrometallurgical methods such as electrolytic refining or recovery are used.
  • the electrowinning and electrorefining processes are current methods to recover the metals, such as copper, zinc, cobalt or nickel.
  • electrolytic refining impure metal anodes are dissolved electrochemically, and the metal dissolved from them is reduced onto the cathode.
  • electrolytic recovery the metal is reduced directly from the electrolytic solution.
  • the cathodes used in the process can be starter sheets made of the metal to be reduced, or permanent cathodes made of stainless steel, for example.
  • a transition to the use of permanent cathodes has been the prevailing trend at electrolytic plants for a long time, and in practice, e.g. all new copper electrolysis processes are based on this technology.
  • a permanent cathode is formed of a cathode plate and an attached suspension bar using which the cathode is suspended in the electrolytic bath.
  • the deposited metal can be mechanically stripped from the surfaces of permanent cathode plate, and the permanent cathodes can be reused.
  • Permanent cathodes can be used in both electrolytic refining and recovery of metals.
  • the corrosion resistance of the steel grade used as a permanent cathode plate in the electrolyte is not enough to guarantee that the properties required of the cathode are fulfilled. Substantial attention must be paid to the adhesion properties of the cathode plate surface.
  • the surface properties of a permanent cathode plate must be appropriate so that the depositing metal does not spontaneously strip off from the surface during the electrolytic process but adheres sufficiently, however not preventing the deposited metal from being removed using a stripping machine, for example.
  • the most important properties required of a permanent cathode plate include corrosion resistance, straightness and surface properties with regard to the adhesion and removability (strippability) of the deposited metal.
  • the permanent cathode plates deteriorate by the chemical (corrosion) and mechanical (bending and hammering during stripping) effects to such a condition that the surface properties may not any more fulfill the requirements of sufficient adhesion and removability.
  • cruds and mottles are formed on the surfaces of the permanent cathode plate and the surface quality deteriorates during lifetime due to scratches and dents generated in use and corrosion. Therefore the permanent cathode does not any more function optimally and adhesion problems may occur.
  • FIGS. 1 to 4 Examples of the deteriorated surfaces of the permanent cathode plates are shown in FIGS. 1 to 4 .
  • FIG. 1 shows how a used and deteriorated permanent cathode plate looks like visually seen by eye. The plate is severely mottled.
  • FIG. 2 shows a microscopic view of the used and deteriorated permanent cathode plate showing the copper arsenide crud covering the surface. Grain boundaries under the crud are barely visible.
  • FIG. 3 shows a microscopic view of the used and deteriorated permanent cathode plate showing black and white crud on the surface. Grain boundaries under the crud are barely visible.
  • FIG. 4 shows a microscopic view of the used permanent cathode plate surface after the crud has been removed. Pitting corrosion on the grain boundaries can be seen making the grain boundaries overly wide and deep and non-optimal with respect to adhesion and strippability.
  • the currently available maintenance by grinding affects only the macro roughness of the surface of the permanent cathode plate, said macro roughness having only a secondary role to the functionality of the permanent cathode plate. Further, the microscopic sharp formations on surface caused by grinding are disadvantageous from the point of view of crud accumulation, corrosion resistance and current distribution which may explain the rapid degradation of the quality of the merely ground surface in use. Therefore, prolonging of the lifetime of the permanent cathodes only by the currently available method does not provide a durable and long-lasting result.
  • the objective of the invention is to alleviate the disadvantages mentioned above.
  • the present invention provides a method for maintenance of used permanent cathode plates, said used cathode plate having scratches, crud formations and oversize grain boundaries on a surface of the cathode plate, the method comprising a step of removing of scratches and accumulated crud from the surface of the cathode plate.
  • the method comprises removing substantially completely the oversize grain boundaries from the surface, and thereafter regenerating the grain boundaries of the surface of the cathode plate to an average grain boundary width of 1 to 3 ⁇ m and an average grain boundary depth less than 1 ⁇ m.
  • the advantage of the invention is that old used permanent cathode plates which otherwise would be at the end of their lifetime can be repaired to substantially correspond to the new ones in order to prolong their lifetime.
  • an electrolysis plant typically has about 30 000 permanent cathode plates. If all these are at the same time coming to the end of their lifetime, it is a large investment to renew all these. With the aid of the method of the present invention it is possible to allocate renewal investment costs of the permanent cathode plates to several years.
  • the method is suitable for maintaining permanent cathode plates made of stainless steel, such as ferritic, austenitic or duplex stainless steel.
  • the method comprises alkaline treatment of the surface of the cathode plate for removing the accumulated crud before removing the oversize grain boundaries from the surface of the cathode plate.
  • the method comprises mechanical grinding of the surface of the cathode plate for removing the accumulated crud.
  • method comprises mechanical grinding of the surface of the cathode plate for removing the oversize grain boundaries.
  • the mechanical grinding is performed in two phases comprising a first phase grinding to surface roughness Ra of about 0.9-1.1 ⁇ m and thereafter a second phase grinding to surface roughness Ra of about 0.2-0.4 ⁇ m.
  • the mechanical grinding is implemented by belt grinding and/or by circular grinding.
  • the alkaline treatment of the surface comprises subjecting the surface to liquid caustic soda (NaOH) having pH>10 or to potassium hydroxide (KOH).
  • NaOH liquid caustic soda
  • KOH potassium hydroxide
  • the alkaline treatment of the surface comprises subjecting the surface to 10M liquid caustic soda (NaOH) in temperature 50° C.
  • regenerating of the grain boundaries of the surface of the cathode plate is made chemically or electrochemically.
  • the electrochemical regenerating of the grain boundaries comprises etching the plate surface with nitric acid 60% solution (HNO 3 ) using current 15-40 As/cm 2 , preferably 20 As/cm 2 .
  • the chemical regenerating of the grain boundaries comprises subjecting the plate surface to oxalic acid (H 2 C 2 O 4 ) or to sulphuric acid (H 2 SO 4 ) or to sulphuric acid-based copper electrolyte.
  • the electrochemical regenerating of the grain boundaries comprises subjecting the plate surface to sulphuric acid-based electrolyte obtained from electrolysis.
  • the sulphuric acid-based electrolyte is advantageous because it is readily available in electrolysis plants.
  • the electrochemical regenerating of the grain boundaries comprises etching the plate surface with sulphuric acid-based electrolyte using current 10-40 As/cm 2 , preferably 20 As/cm 2 .
  • the method comprises passivation of the surface after regeneration of the grain boundaries.
  • the passivation of the surface comprises dipping the cathode plate into nitric acid (HNO 3 ) or citric acid (C 6 H 8 O 7 ).
  • the method comprises neutralizing and washing of the surface to neutralize and wash out the nitric acid or citric acid after passivation.
  • FIG. 1 is a photographic image of a used and deteriorated permanent cathode plate
  • FIG. 2 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with copper arsenide crud on the surface,
  • FIG. 3 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with black and white crud on the surface, and
  • FIG. 4 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with pitting corrosion on grain boundaries.
  • FIG. 5 is a microscopic image showing a microscopic view of the used permanent cathode surface after mechanical grinding
  • FIG. 6 is a microscopic image showing a microscopic view of a copper replica of the treated permanent cathode surface in which the too long time in electrolytic etching has created too deep grain boundaries, and
  • FIG. 7 is a microscopic image showing the modification of the grain boundaries with time when electrolytically etching in copper electrolyte.
  • a used permanent cathode plate has scratches, crud formations and oversize grain boundaries on the surface of the cathode plate. Therefore, in the method for maintenance of used permanent cathode plates, scratches and accumulated crud are first removed from the surface of the cathode plate. Removing of the crud may be made by alkaline treatment of the surface of the permanent cathode plate. In the alkaline treatment the surface of the permanent cathode plate may be subjected to 10M liquid caustic soda (NaOH) having pH>10 in temperature 50° C. Alternatively, the alkaline treatment may be made by subjecting the surface of the permanent cathode plate to potassium hydroxide (KOH).
  • NaOH liquid caustic soda
  • KOH potassium hydroxide
  • Alkaline treatment is not necessary if the surface of the permanent cathode plate is subjected to mechanical grinding which may be used for removing the scratches, crud formations and also the grain boundaries from the surface. It is essential to remove substantially completely the oversize grain boundaries from the surface.
  • the mechanical grinding is preferably performed in two phases comprising a first phase grinding to surface roughness Ra of about 0.9-1.1 ⁇ m and thereafter a second phase grinding to surface roughness Ra of about 0.2-0.4 ⁇ m.
  • the mechanical grinding may be made by belt grinding or circular grinding or any other suitable grinding method.
  • the grain boundaries of the surface of the cathode plate are regenerated to their optimal dimensions, an average grain boundary width being 1 to 3 ⁇ m and an average grain boundary depth being less than 1 ⁇ m.
  • the regenerating of the grain boundaries can be made electrochemically or chemically.
  • the electrochemical regenerating of the grain boundaries of 316L stainless steel comprises subjecting the plate surface to nitric acid 60% solution (HNO 3 ) using current 15-40 As/cm 2 , preferably 20 As/cm 2 .
  • the chemical regenerating of the grain boundaries comprises subjecting the plate surface to oxalic acid (H 2 C 2 O 4 ) or to sulphuric acid (H 2 SO 4 ) or to sulphuric acid-based electrolyte.
  • sulphuric acid-based electrolyte When regenerating of the grain boundaries is made by etching the plate surface with sulphuric acid-based electrolyte, current 10-40 As/cm 2 , preferably 20 As/cm 2 , is used.
  • the sulphuric acid-based electrolyte is advantageous because it is readily available in electrolysis plants.
  • the acid content of electrolyte is 140-200 g/l and copper content 30-60 g/l.
  • the surface may further be passivated.
  • the passivation of the surface may include dipping the cathode plate into nitric acid (HNO 3 ) or to citric acid (C 6 H 8 O 7 ). After passivation it may be appropriate to neutralize and wash the surface to neutralize and wash out the acid.
  • the used permanent cathode plate subjected to the maintenance method of the invention is substantially as good as a new one and thus its lifetime may be prolonged for another 10 to 15 years.
  • FIG. 5 shows an optical microscope image of the ground surface.
  • the stripping force needed for the deposited copper was only 0.5 N/mm 2 . This value is too low compared to the typical value of 1.0 N/mm 2 for a new permanent cathode surface.
  • the surface was electrolytically etched in 60% nitric acid using a current density of 18 mA/cm 2 and a total current of 20 As/cm 2 to modify the grain boundaries. After etching an electrorefining and stripping test similar made to the bare ground surface was made. Measured stripping force copper deposit was now 1.1 N/mm 2 which is close enough to the value measured for copper deposit from a new permanent cathode surface.
  • a used 316L permanent cathode surface was ground and electrically etched in 60% nitric acid using a current density of 18 mA/cm 2 and a total current of 41 As/cm 2 . After etching a small scale copper electrorefining and stripping test was made. The measured stripping force for copper deposit was higher than 3.0 N/mm 2 which is far too high. The surface of the copper deposit close to the etched permanent cathode surface was viewed with a microscope to see what has happened to the grain boundaries during etching. It can be seen that the depth of the grain boundaries has increased too much and this was the reason for the too high stripping force obtained.
  • FIG. 6 shows a copper replica of the surface whose grain boundaries were etched too deep.
  • electrolytic etching was performed in 150 g/l sulphuric acid with 50 g/l copper which corresponds to the electrolyte that is typically used in copper electrolysis.
  • Etching with currents of 10-60 As/cm 2 influenced the width and depth of the grain boundaries as a function of time as demonstrated in FIG. 7 .
  • the current density and treatment time are specific to a certain stainless steel grade but can be selected based on the dimensions of the grain boundaries.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Engineering & Computer Science (AREA)
  • Electrolytic Production Of Metals (AREA)
  • ing And Chemical Polishing (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Prevention Of Electric Corrosion (AREA)

Abstract

A method for maintenance of used permanent cathode plates, said used cathode plate having scratches, crud formations and oversize grain boundaries on a surface of the cathode plate. The method comprises removing of scratches and accumulated crud from the surface of the cathode plate. The method further comprises removing substantially completely the oversize grain boundaries from the surface, and thereafter regenerating the grain boundaries of the surface of the cathode plate to an average grain boundary width of 1 to 3 μm and an average grain boundary depth less than 1 μm.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a National Phase Entry under 35 USC §371 of PCT Patent Application Serial No. PCT/FI2014/051005 filed Dec. 16, 2014, which claims the benefit under 35 USC §119(e) to Finnish Patent Application No. 20136286, filed Dec. 18, 2013, the disclosure of each of these applications are expressly incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
The present invention relates to a method for maintenance of used permanent cathode plates.
BACKGROUND OF THE INVENTION
When the intention is to manufacture pure metal such as copper, hydrometallurgical methods such as electrolytic refining or recovery are used. The electrowinning and electrorefining processes are current methods to recover the metals, such as copper, zinc, cobalt or nickel. In electrolytic refining, impure metal anodes are dissolved electrochemically, and the metal dissolved from them is reduced onto the cathode. In electrolytic recovery, the metal is reduced directly from the electrolytic solution. The cathodes used in the process can be starter sheets made of the metal to be reduced, or permanent cathodes made of stainless steel, for example. A transition to the use of permanent cathodes has been the prevailing trend at electrolytic plants for a long time, and in practice, e.g. all new copper electrolysis processes are based on this technology.
A permanent cathode is formed of a cathode plate and an attached suspension bar using which the cathode is suspended in the electrolytic bath. The deposited metal can be mechanically stripped from the surfaces of permanent cathode plate, and the permanent cathodes can be reused. Permanent cathodes can be used in both electrolytic refining and recovery of metals. The corrosion resistance of the steel grade used as a permanent cathode plate in the electrolyte is not enough to guarantee that the properties required of the cathode are fulfilled. Substantial attention must be paid to the adhesion properties of the cathode plate surface. The surface properties of a permanent cathode plate must be appropriate so that the depositing metal does not spontaneously strip off from the surface during the electrolytic process but adheres sufficiently, however not preventing the deposited metal from being removed using a stripping machine, for example.
The most important properties required of a permanent cathode plate include corrosion resistance, straightness and surface properties with regard to the adhesion and removability (strippability) of the deposited metal.
During years in operation the permanent cathode plates deteriorate by the chemical (corrosion) and mechanical (bending and hammering during stripping) effects to such a condition that the surface properties may not any more fulfill the requirements of sufficient adhesion and removability. In operation, cruds and mottles are formed on the surfaces of the permanent cathode plate and the surface quality deteriorates during lifetime due to scratches and dents generated in use and corrosion. Therefore the permanent cathode does not any more function optimally and adhesion problems may occur.
So far, the only solution to prolong the lifetime of the permanent cathodes has been the maintenance of the permanent cathode plates by subjecting them to periodical repair where the accumulated crud and scratches are removed from the surfaces by grinding and the edge insulation is replaced. The permanent cathode plate may also be straightened if required. The problem with the current method is that, in practice, it has proved that such a treatment solves the problem only momentarily.
It is known, that in addition to the macro roughness of the surface, which is a commonly measured characteristics and which is changed in grinding, also the characteristics of the grain boundaries have a significant role for the adhesion and strippability of the deposited metal because the grain boundaries in micro scale serve as adhesion points for the depositing metal. The depth and width of the grain boundaries must be in a certain relation to each other so that the depositing metal adheres sufficiently but not too tightly to the surface of the permanent cathode plate. A prior art document WO 2012/175803 A2 discloses preferable grain boundary dimensions for permanent cathode plates.
In operation, impurities and cruds are precipitated on the grain boundaries and on the grain interiors and also the corrosion changes the micro structure so that the grain boundaries become oversize, i.e. overly deep and/or wide, whereby optimal surface characteristics are lost.
Examples of the deteriorated surfaces of the permanent cathode plates are shown in FIGS. 1 to 4. FIG. 1 shows how a used and deteriorated permanent cathode plate looks like visually seen by eye. The plate is severely mottled. FIG. 2 shows a microscopic view of the used and deteriorated permanent cathode plate showing the copper arsenide crud covering the surface. Grain boundaries under the crud are barely visible. FIG. 3 shows a microscopic view of the used and deteriorated permanent cathode plate showing black and white crud on the surface. Grain boundaries under the crud are barely visible. FIG. 4 shows a microscopic view of the used permanent cathode plate surface after the crud has been removed. Pitting corrosion on the grain boundaries can be seen making the grain boundaries overly wide and deep and non-optimal with respect to adhesion and strippability.
The currently available maintenance by grinding affects only the macro roughness of the surface of the permanent cathode plate, said macro roughness having only a secondary role to the functionality of the permanent cathode plate. Further, the microscopic sharp formations on surface caused by grinding are disadvantageous from the point of view of crud accumulation, corrosion resistance and current distribution which may explain the rapid degradation of the quality of the merely ground surface in use. Therefore, prolonging of the lifetime of the permanent cathodes only by the currently available method does not provide a durable and long-lasting result.
OBJECTIVE OF THE INVENTION
The objective of the invention is to alleviate the disadvantages mentioned above.
In particular, it is an objective of the present invention to provide a method which produces an optimal surface quality for the used permanent cathode plate which corresponds to the surface quality of an unused permanent cathode plate with appropriate adhesion and strippability characteristics thus providing a significant prolonging of the lifetime of the permanent cathode plate.
SUMMARY OF THE INVENTION
According to an aspect, the present invention provides a method for maintenance of used permanent cathode plates, said used cathode plate having scratches, crud formations and oversize grain boundaries on a surface of the cathode plate, the method comprising a step of removing of scratches and accumulated crud from the surface of the cathode plate. According to the invention the method comprises removing substantially completely the oversize grain boundaries from the surface, and thereafter regenerating the grain boundaries of the surface of the cathode plate to an average grain boundary width of 1 to 3 μm and an average grain boundary depth less than 1 μm.
The advantage of the invention is that old used permanent cathode plates which otherwise would be at the end of their lifetime can be repaired to substantially correspond to the new ones in order to prolong their lifetime. For example, an electrolysis plant typically has about 30 000 permanent cathode plates. If all these are at the same time coming to the end of their lifetime, it is a large investment to renew all these. With the aid of the method of the present invention it is possible to allocate renewal investment costs of the permanent cathode plates to several years.
The method is suitable for maintaining permanent cathode plates made of stainless steel, such as ferritic, austenitic or duplex stainless steel.
In an embodiment of the invention, the method comprises alkaline treatment of the surface of the cathode plate for removing the accumulated crud before removing the oversize grain boundaries from the surface of the cathode plate.
In an embodiment of the invention, the method comprises mechanical grinding of the surface of the cathode plate for removing the accumulated crud.
In an embodiment of the invention, method comprises mechanical grinding of the surface of the cathode plate for removing the oversize grain boundaries.
In an embodiment of the invention, the mechanical grinding is performed in two phases comprising a first phase grinding to surface roughness Ra of about 0.9-1.1 μm and thereafter a second phase grinding to surface roughness Ra of about 0.2-0.4 μm.
In an embodiment of the invention, the mechanical grinding is implemented by belt grinding and/or by circular grinding.
In an embodiment of the invention, the alkaline treatment of the surface comprises subjecting the surface to liquid caustic soda (NaOH) having pH>10 or to potassium hydroxide (KOH).
In an embodiment of the invention, the alkaline treatment of the surface comprises subjecting the surface to 10M liquid caustic soda (NaOH) in temperature 50° C.
In an embodiment of the invention, regenerating of the grain boundaries of the surface of the cathode plate is made chemically or electrochemically.
In an embodiment of the invention, the electrochemical regenerating of the grain boundaries comprises etching the plate surface with nitric acid 60% solution (HNO3) using current 15-40 As/cm2, preferably 20 As/cm2.
In an embodiment of the invention, the chemical regenerating of the grain boundaries comprises subjecting the plate surface to oxalic acid (H2C2O4) or to sulphuric acid (H2SO4) or to sulphuric acid-based copper electrolyte.
In an embodiment of the invention, the electrochemical regenerating of the grain boundaries comprises subjecting the plate surface to sulphuric acid-based electrolyte obtained from electrolysis. The sulphuric acid-based electrolyte is advantageous because it is readily available in electrolysis plants.
In an embodiment of the invention, the electrochemical regenerating of the grain boundaries comprises etching the plate surface with sulphuric acid-based electrolyte using current 10-40 As/cm2, preferably 20 As/cm2.
In an embodiment of the invention, the method comprises passivation of the surface after regeneration of the grain boundaries.
In an embodiment of the invention, the passivation of the surface comprises dipping the cathode plate into nitric acid (HNO3) or citric acid (C6H8O7).
In an embodiment of the invention, the method comprises neutralizing and washing of the surface to neutralize and wash out the nitric acid or citric acid after passivation.
It is to be understood that the aspects and embodiments of the invention described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the invention.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a photographic image of a used and deteriorated permanent cathode plate,
FIG. 2 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with copper arsenide crud on the surface,
FIG. 3 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with black and white crud on the surface, and
FIG. 4 is a microscopic image showing a microscopic view of the surface of the used and deteriorated permanent cathode plate with pitting corrosion on grain boundaries.
FIG. 5 is a microscopic image showing a microscopic view of the used permanent cathode surface after mechanical grinding,
FIG. 6 is a microscopic image showing a microscopic view of a copper replica of the treated permanent cathode surface in which the too long time in electrolytic etching has created too deep grain boundaries, and
FIG. 7 is a microscopic image showing the modification of the grain boundaries with time when electrolytically etching in copper electrolyte.
 DETAILED DESCRIPTION OF THE INVENTION
A used permanent cathode plate has scratches, crud formations and oversize grain boundaries on the surface of the cathode plate. Therefore, in the method for maintenance of used permanent cathode plates, scratches and accumulated crud are first removed from the surface of the cathode plate. Removing of the crud may be made by alkaline treatment of the surface of the permanent cathode plate. In the alkaline treatment the surface of the permanent cathode plate may be subjected to 10M liquid caustic soda (NaOH) having pH>10 in temperature 50° C. Alternatively, the alkaline treatment may be made by subjecting the surface of the permanent cathode plate to potassium hydroxide (KOH). Alkaline treatment is not necessary if the surface of the permanent cathode plate is subjected to mechanical grinding which may be used for removing the scratches, crud formations and also the grain boundaries from the surface. It is essential to remove substantially completely the oversize grain boundaries from the surface. The mechanical grinding is preferably performed in two phases comprising a first phase grinding to surface roughness Ra of about 0.9-1.1 μm and thereafter a second phase grinding to surface roughness Ra of about 0.2-0.4 μm. The mechanical grinding may be made by belt grinding or circular grinding or any other suitable grinding method.
After the removal of the grain boundaries, the grain boundaries of the surface of the cathode plate are regenerated to their optimal dimensions, an average grain boundary width being 1 to 3 μm and an average grain boundary depth being less than 1 μm. The regenerating of the grain boundaries can be made electrochemically or chemically. The electrochemical regenerating of the grain boundaries of 316L stainless steel comprises subjecting the plate surface to nitric acid 60% solution (HNO3) using current 15-40 As/cm2, preferably 20 As/cm2.
Alternatively, the chemical regenerating of the grain boundaries comprises subjecting the plate surface to oxalic acid (H2C2O4) or to sulphuric acid (H2SO4) or to sulphuric acid-based electrolyte.
When regenerating of the grain boundaries is made by etching the plate surface with sulphuric acid-based electrolyte, current 10-40 As/cm2, preferably 20 As/cm2, is used. The sulphuric acid-based electrolyte is advantageous because it is readily available in electrolysis plants. Typically the acid content of electrolyte is 140-200 g/l and copper content 30-60 g/l.
After the regenerating of the grain boundaries, the surface may further be passivated. The passivation of the surface may include dipping the cathode plate into nitric acid (HNO3) or to citric acid (C6H8O7). After passivation it may be appropriate to neutralize and wash the surface to neutralize and wash out the acid.
The used permanent cathode plate subjected to the maintenance method of the invention is substantially as good as a new one and thus its lifetime may be prolonged for another 10 to 15 years.
EXAMPLES Example 1
A used permanent cathode surface was first cleaned with mechanical grinding to remove the accumulated crud. FIG. 5 shows an optical microscope image of the ground surface. When this ground surface was tested in a small scale copper refining and stripping test the stripping force needed for the deposited copper was only 0.5 N/mm2. This value is too low compared to the typical value of 1.0 N/mm2 for a new permanent cathode surface. Then the surface was electrolytically etched in 60% nitric acid using a current density of 18 mA/cm2 and a total current of 20 As/cm2 to modify the grain boundaries. After etching an electrorefining and stripping test similar made to the bare ground surface was made. Measured stripping force copper deposit was now 1.1 N/mm2 which is close enough to the value measured for copper deposit from a new permanent cathode surface.
Example 2
A used 316L permanent cathode surface was ground and electrically etched in 60% nitric acid using a current density of 18 mA/cm2 and a total current of 41 As/cm2. After etching a small scale copper electrorefining and stripping test was made. The measured stripping force for copper deposit was higher than 3.0 N/mm2 which is far too high. The surface of the copper deposit close to the etched permanent cathode surface was viewed with a microscope to see what has happened to the grain boundaries during etching. It can be seen that the depth of the grain boundaries has increased too much and this was the reason for the too high stripping force obtained. FIG. 6 shows a copper replica of the surface whose grain boundaries were etched too deep.
Example 3
As nitric acid is not commonly used in copper refineries and it has relatively small time window to produce an optimal cathode surface, electrolytic etching was performed in 150 g/l sulphuric acid with 50 g/l copper which corresponds to the electrolyte that is typically used in copper electrolysis. Etching with currents of 10-60 As/cm2 influenced the width and depth of the grain boundaries as a function of time as demonstrated in FIG. 7. The current density and treatment time are specific to a certain stainless steel grade but can be selected based on the dimensions of the grain boundaries.
When using copper electrolyte in the electrolytical etching stainless steel plates can be used as cathodes. Copper will be deposited on them but if needed it can be dissolved or mechanically stripped off.

Claims (16)

The invention claimed is:
1. A method for maintenance of used permanent cathode plates made of stainless steel, said used cathode plate having scratches, crud formations and oversize grain boundaries on a surface of the cathode plate, the method comprising:
removing of scratches and accumulated crud from the surface of the cathode plate,
removing substantially completely the oversize grain boundaries from the surface, and thereafter
regenerating the grain boundaries of the surface of the cathode plate to an average grain boundary width of 1 to 3 μm and an average grain boundary depth less than 1 μm.
2. The method according to claim 1, further comprising alkaline treatment of the surface of the cathode plate for removing the accumulated crud before removing the oversize grain boundaries from the surface of the cathode plate.
3. The method according to claim 1, further comprising mechanical grinding of the surface of the cathode plate for removing the accumulated crud.
4. The method according to claim 1, further comprising mechanical grinding of the surface of the cathode plate for removing the oversize grain boundaries.
5. The method according to claim 1, further comprising mechanical grinding of the surface of the cathode plate wherein the mechanical grinding is performed in two phases comprising a first phase grinding to surface roughness Ra of about 0.9-1.1 μm and thereafter a second phase grinding to surface roughness Ra of about 0.2-0.4 μm.
6. The method according to claim 5, wherein the mechanical grinding is implemented by at least one of belt grinding and circular grinding.
7. The method according to claim 2, wherein, the alkaline treatment of the surface comprises subjecting the surface to liquid caustic soda (NaOH) having a pH greater than at least one of 10 and a pH of potassium hydroxide (KOH).
8. The method according to claim 7, wherein the alkaline treatment of the surface comprises subjecting the surface to 10M liquid caustic soda (NaOH) at a temperature of 50° C.
9. The method according to claim 1, wherein regenerating of the grain boundaries of the surface of the cathode plate is performed by at least one of the chemically and electrochemically.
10. The method according to claim 1, wherein the electrochemical regenerating of the grain boundaries comprises etching the plate surface with nitric acid 60% solution (HNO3) using a current of 15-40 As/cm2, and preferably 20 As/cm2.
11. The method according to claim 1, wherein the chemical regenerating of the grain boundaries comprises subjecting the plate surface to at least one of oxalic acid (H2C2O4) and sulphuric acid (H2SO4) and sulphuric acid-based copper electrolyte.
12. The method according to claim 1, wherein the electrochemical regenerating of the grain boundaries comprises subjecting the plate surface to sulphuric acid-based electrolyte obtained from electrolysis.
13. The method according to claim 1, wherein the electrochemical regenerating of the grain boundaries comprises etching the plate surface with sulphuric acid-based electrolyte using current 10-40 As/cm2, preferably 20 As/cm2.
14. The method according to claim 1, further comprising passivation of the surface after regeneration of the grain boundaries.
15. The method according to claim 14, wherein the passivation of the surface comprises dipping the cathode plate into nitric acid (HNO3) or citric acid (C6H8O7).
16. The method according to claim 15, further comprising neutralizing and washing of the surface to neutralize and wash out the nitric acid or citric acid after passivation.
US15/104,312 2013-12-18 2014-12-16 Method for maintenance of used permanent cathode plates Active US9708725B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI20136286A FI125980B (en) 2013-12-18 2013-12-18 Procedure for maintenance of used cathode plates
FI20136286 2013-12-18
PCT/FI2014/051005 WO2015092133A1 (en) 2013-12-18 2014-12-16 Method for maintenance of used permanent cathode plates

Publications (2)

Publication Number Publication Date
US20160312376A1 US20160312376A1 (en) 2016-10-27
US9708725B2 true US9708725B2 (en) 2017-07-18

Family

ID=52339153

Family Applications (1)

Application Number Title Priority Date Filing Date
US15/104,312 Active US9708725B2 (en) 2013-12-18 2014-12-16 Method for maintenance of used permanent cathode plates

Country Status (12)

Country Link
US (1) US9708725B2 (en)
EP (1) EP3084041B1 (en)
JP (1) JP6271740B2 (en)
CN (1) CN105874104B (en)
AP (1) AP2016009295A0 (en)
AU (1) AU2014369686B2 (en)
CL (1) CL2016001506A1 (en)
EA (1) EA031570B1 (en)
ES (1) ES2702186T3 (en)
FI (1) FI125980B (en)
MX (1) MX377863B (en)
WO (1) WO2015092133A1 (en)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10458037B2 (en) * 2015-10-27 2019-10-29 Georgia Tech Research Corporation Systems and methods for producing anti-wetting structures on metallic surfaces
CN106521562A (en) * 2016-09-30 2017-03-22 云南铜业股份有限公司 Recovery method of copper electrolysis permanent stainless steel cathode
JP7196574B2 (en) * 2018-11-30 2022-12-27 住友金属鉱山株式会社 Cathode plate for electrolysis and electrorefining method using the same
DE102020204431A1 (en) * 2020-04-06 2021-10-07 Aesculap Ag Method for surface treatment and / or production of a medical technology product and a medical technology product

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3741747A (en) 1971-09-30 1973-06-26 Amchem Prod Highly alkaline titanated cleaner
US4139430A (en) * 1976-04-01 1979-02-13 Ronald Parkinson Process of electrodeposition and product utilizing a reusable integrated cathode unit
JPH05255884A (en) 1992-03-10 1993-10-05 Sumitomo Metal Mining Co Ltd Method for repairing stainless steel cathode plate for electrolysis of copper
EP1336670A2 (en) 2002-02-13 2003-08-20 Ineos Chlor Limited Plate treatment
EP1531014A2 (en) 2003-11-11 2005-05-18 Fuji Photo Film Co., Ltd. Roll for metal rolling, and support for lithographic printing plate
CN1780939A (en) 2003-04-29 2006-05-31 埃克斯特阿特昆士兰有限公司 Method and apparatus for manufacturing cathode plates
US20060201586A1 (en) * 2005-03-09 2006-09-14 Xstrata Queensland Limited Stainless steel electrolytic plates
CN101501914A (en) 2006-08-14 2009-08-05 东洋制罐株式会社 Stainless steel member for fuel cell
CN101611175A (en) 2007-02-13 2009-12-23 奥图泰有限公司 Manufacturing method of cathode plate and cathode plate
WO2010102327A1 (en) 2009-03-12 2010-09-16 Steelmore Holdings Pty Ltd A method of reconditioning a cathode plate
US20120164472A1 (en) * 2009-08-25 2012-06-28 Thyssenkrupp Steel Europe Ag Method of Producing a Steel Component Provided with a Metallic Coating Giving Protection Against Corrosion, and a Steel Component
WO2012175803A2 (en) 2011-06-23 2012-12-27 Outotec Oyj Permanent cathode and a method for treating the surface of a permanent cathode

Patent Citations (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3741747A (en) 1971-09-30 1973-06-26 Amchem Prod Highly alkaline titanated cleaner
US4139430A (en) * 1976-04-01 1979-02-13 Ronald Parkinson Process of electrodeposition and product utilizing a reusable integrated cathode unit
JPH05255884A (en) 1992-03-10 1993-10-05 Sumitomo Metal Mining Co Ltd Method for repairing stainless steel cathode plate for electrolysis of copper
EP1336670A2 (en) 2002-02-13 2003-08-20 Ineos Chlor Limited Plate treatment
CN1780939A (en) 2003-04-29 2006-05-31 埃克斯特阿特昆士兰有限公司 Method and apparatus for manufacturing cathode plates
US20100219080A1 (en) * 2003-04-29 2010-09-02 Xstrata Queensland Limited Methods and apparatus for cathode plate production
EP1531014A2 (en) 2003-11-11 2005-05-18 Fuji Photo Film Co., Ltd. Roll for metal rolling, and support for lithographic printing plate
JP2008533296A (en) 2005-03-09 2008-08-21 エクストラータ クイーンズランド リミテッド Stainless steel electrolytic plate
CN101166850A (en) 2005-03-09 2008-04-23 斯特拉塔昆士兰有限公司 Stainless steel electrolytic plate
US20060201586A1 (en) * 2005-03-09 2006-09-14 Xstrata Queensland Limited Stainless steel electrolytic plates
CN101501914A (en) 2006-08-14 2009-08-05 东洋制罐株式会社 Stainless steel member for fuel cell
US20100189997A1 (en) * 2006-08-14 2010-07-29 Toyo Seikan Kaisha, Ltd. Stainless steel member for a fuel cell
CN101611175A (en) 2007-02-13 2009-12-23 奥图泰有限公司 Manufacturing method of cathode plate and cathode plate
US20100078319A1 (en) * 2007-02-13 2010-04-01 Outotec Oyj Method of manufacturing a cathode plate, and a cathode plate
WO2010102327A1 (en) 2009-03-12 2010-09-16 Steelmore Holdings Pty Ltd A method of reconditioning a cathode plate
US20120164472A1 (en) * 2009-08-25 2012-06-28 Thyssenkrupp Steel Europe Ag Method of Producing a Steel Component Provided with a Metallic Coating Giving Protection Against Corrosion, and a Steel Component
CN102625863A (en) 2009-08-25 2012-08-01 蒂森克虏伯钢铁欧洲股份公司 Method for producing a steel component provided with a metal coating protecting against corrosion and steel component
WO2012175803A2 (en) 2011-06-23 2012-12-27 Outotec Oyj Permanent cathode and a method for treating the surface of a permanent cathode
US20140131221A1 (en) * 2011-06-23 2014-05-15 Outotec Oyj Permanent cathode and a method for treating the surface of a permanent cathode

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
Chinese Office Action entitled Notification of First Office Action issued by the State Intellectual Property Office of the People's Republic of China in relation to Chinese Applicaiton No. 201480072269.9 dated Apr. 24, 2017 (5 pages) along with English language translation (6 pages).
International Search Report issued by the European Patent Office acting as the International Search Authority for International Application No. PCT/FI2014/051005 dated Apr. 10, 2015 (3 pages).
Japanese Office Action entitled Notification of Reason for Refusal issued by the Japanese Patent Office in relation to Japanese Patent Application No. 2016-540496 dated Apr. 18, 2017 (3 pages) along with English language translation 3 pages).
Notification of Transmittal of the International Preliminary Report on Patentability issued by the European Patent Office acting as the International Preliminary Examining Authority for International Application No. PCT/FI2014/051005 dated Jan. 8, 2016 (14 pages).
Written Opinion of the International Searching Authority issued by the European Patent Office acting as the International Search Authority for International Application No. PCT/FI2014/051005 (6 pages).

Also Published As

Publication number Publication date
AU2014369686A1 (en) 2016-07-07
CL2016001506A1 (en) 2016-12-02
ES2702186T3 (en) 2019-02-27
AP2016009295A0 (en) 2016-06-30
FI20136286A7 (en) 2015-06-19
EA201691080A1 (en) 2016-11-30
CN105874104A (en) 2016-08-17
JP2017503921A (en) 2017-02-02
EP3084041A1 (en) 2016-10-26
US20160312376A1 (en) 2016-10-27
EA031570B1 (en) 2019-01-31
FI125980B (en) 2016-05-13
JP6271740B2 (en) 2018-01-31
MX2016007893A (en) 2016-09-13
MX377863B (en) 2025-03-11
AU2014369686B2 (en) 2017-03-09
WO2015092133A1 (en) 2015-06-25
EP3084041B1 (en) 2018-09-26
CN105874104B (en) 2018-02-13

Similar Documents

Publication Publication Date Title
US9708725B2 (en) Method for maintenance of used permanent cathode plates
KR100371524B1 (en) Surface roughening treatment method of copper foil
JP5094172B2 (en) Aluminum base material for etching and aluminum electrode material for electrolytic capacitor using the same
US8062498B2 (en) Method of manufacturing a cathode plate, and a cathode plate
US20110253554A1 (en) Electrolyte for removing titanium-containing coatings and removing method using same
CN102234835B (en) Stripping solution and method for stripping titanium carbide film layer by electrolysis
JP2015518925A (en) Method for making a metal coating
US20140034514A1 (en) Electrolyte for removing metal-carbide/nitride coatings or metal-carbide-nitride coatings and removing method using same
CN103774193A (en) Method for electrolytic-depositing dispersed zinc crystal nucleuses on surface of medium-high voltage electronic aluminum foil
JP3955933B2 (en) Method for adjusting the outer surface of a continuous casting mold made of copper or a copper alloy including a nickel plating step and a nickel removal step
CN102234833B (en) Stripping solution and method for electrolytically removing chromium carbide film
CN103748267A (en) A permanent cathode and a method for treating the surface of a permanent cathode
JP5613125B2 (en) Method for producing aluminum anodic oxide film having high withstand voltage and excellent productivity
CN109097817B (en) Method and device for improving wave edge of low-voltage anode foil
JP2011208261A (en) Cathode plate, method of manufacturing cathode plate and method for metal electrolytic refining
CN111094632B (en) Method for electrolytically depositing a zinc-nickel alloy layer on at least one substrate to be treated
JP4280593B2 (en) Copper electrolytic purification method
Barmi The development and testing of alternative anodes based on cobalt and lead for the electrowinning of base metals
JP2005187833A (en) Method for electrolytic purification of metals
JP2006257525A (en) Method for regenerating copper fluoroborate plating waste solution
JPH09143794A (en) Formation of high-lubricating anodically oxidized film of aluminum

Legal Events

Date Code Title Description
AS Assignment

Owner name: OUTOTEC (FINLAND) OY, FINLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LINDGREN, MARI;VIRTANEN, HENRI K.;REEL/FRAME:039239/0143

Effective date: 20160620

STCF Information on status: patent grant

Free format text: PATENTED CASE

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 4TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1551); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 4

AS Assignment

Owner name: METSO MINERALS OY, FINLAND

Free format text: MERGER;ASSIGNOR:OUTOTEC (FINLAND) OY;REEL/FRAME:061685/0481

Effective date: 20210101

Owner name: METSO OUTOTEC FINLAND OY, FINLAND

Free format text: CHANGE OF NAME;ASSIGNOR:METSO MINERALS OY;REEL/FRAME:061685/0552

Effective date: 20210101

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 8TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1552); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 8